USPTO Patents Application 09701705

(19)

J

Europaisches Patentamt
European Patent Office
Office europ^en des brevets

(11)

EP 0 955 741 A1

(12)

EUROPEAN PATENT APPLICATION

published in accordance with Art. 1 58(3) EPC

(43)

Date of publication:

(51)

Int. 01.^: H04J 13/00

iOii i QQQ Ri il latin i QQQ^AI^
1 U.I 1.1 99^7 DUIIclin 1 9i7^/40

(86)

International application number:

(21)

Application number: 98954776.5

PCT/JP98/05241

(22)

Date of filing: 20.11.1998

(87)

International publication number:

WO 99/27672 (03.06.1999 Gazette 1999/22)

(84)

Designated Contracting States:

•

SAWAHASHI, Mamoru

DE FR GB IT SE

Yokohama-Shi, Kanagawa 236-0052 (JP)

ADACHI, Fumiyuki

(30)

Priority: 21.11.1997 JP 32156197

Yokohama-Shi, Kanagawa 236-0052 (JP)

(71)

Applicant:

(74) Representative:

NTT MOBILE COMMUNICATIONS NETWORK

Beresford, Keith Denis Lewis et ai

INC.

BERESFORD & Co.

Minato-ku, Tokyo 105-8436 (JP)

■High Holborn

2-5 Warwick Court

(72)

Inventors:

London WC1R5DJ(GB)

•

ABETA, Sadayuki

Yokosuka-shi, Kanagawa 239-0841 (JP)

lO
O)

o

LU

(54) CHANNEL ESTIMATING APPARATUS, AND CDMA RECEIVER AND CDMA TRANSCEIVER
EACH HAVING THE APPARATUS

(57) There are provided a channel estimation unit
for achieving highly accurate channel estimation, a
CDMA receiver and a CDMA transceiver with the chan-
nel estimation unit. Channel estimates of data symbols
are obtained from a pilot symbol sequence which is par-
allel with a data symbol sequence. First, a plurality of
pilot blocks are generated from the pilot symbol
sequence. The channel estimates of the data symbols
are obtained by calculating a sum of appropriately

weighted averages of pilot symbols in the individual pilot
blocks. This enables highly accurate channel estima-
tion. More accurate channel estimation can be achieved
by carrying out the channel estimation of the data sym-
bols using the pilot symbols belonging to other slots
rather than limiting to the pilot symbols in the slot to
which the estimated data symbol belongs.

(N-K+1)TH
^^3^,gH DATA SYMBOL

nTH DATA SmOL
VKSk SYHBOL^N^DATil SXKBOL

tCni) ^Ois) 5Cn3)

CHANNEL ESUMAIE OF nIH DXTk SYMBOL

FIG.3

Printed by Xerox (UK) Business Services
2.16.7/3.6

EP 0 955 741 A1

Description

TECHNICAL FIELD

5 [0001] The present invention relates to a device for mal^ng channel estimation (propagation path estimation) of data
symbols from a pilot symbol sequence parallel to a data symbol sequence, and a CDMA (Code Division Multiple
Access) receiver and CDMA transmitter with the device.

BACKGROUND ART

10

[0002] In a mobile communications environment, amplitude and phase fluctuations in a traffic channel can occur
because of Rayleigh fading due to changes in the relative location between a mobile station and a base station. Thus,
in a conventional phase modulation scheme that transmits data (information) by the phase of a carrier, it is common for
a transmitting side to carry out differential encoding of transmitted data for impressing the data on relative phases of

15 neighboring symbols, and for a receiving side to discriminate and decide the data by differential detection.

[0003] However, since the transmitted data is subjected to the differential encoding as mentioned above, a one-bit
error in a radio section appears as a two-bit error in the differential detection, thereby increasing the receiving error rate
by 3 dB in terms of the SNIR (Signal-to-Noise Interference power Ratio) as compared with coherent detection like
binary phase-shift keyed modulation (BPSK modulation).

20 [0004] On the other hand, although absolute coherent detection, which discriminates and decides the phase of a
received signal using the absolute phase of each data symbol, has a highly efficient receiving characteristic, it is difficult
under the Rayleigh fading environment to decide the absolute phase of the reception.

[0005] In regard to this matter, Sadayuki Abeta, et al. , "DS/CDM A Coherent Detection System with a Suppressed Pilot
Channel", IEEE GLOBECOM'94, pp. 1622-1626, 1994, proposes a method of estimating fading distortion by inserting,
25 in parallel with a data channel for transmitting data, a pilot channel which is orthogonal to the data channel and has
known phases, thereby compensating for the fading distortion.

[0006] Fig. 13 illustrates a channel estimation method disclosed in this paper. In Fig. 13, the channel estimation is
carried out using a pilot symbol sequence parallel with a data symbol sequence. To reduce a power loss, the power of
the pilot symbol sequence is set less than that of the data symbol sequence.

30 [0007] In addition, to follow instantaneous Rayleigh fluctuations, the transmission power control is carried out on a
slot by slot basis. Accordingly, as shown in Fig. 13, the amplitudes (powers) of the data symbol sequence and pilot sym-
bol sequence vary slot by slot, and their phases also vary slightly due to the operation of amplifiers during transmission.
Such transmission power control enables a reverse channel of the DS-CDMA (Direct Sequence CDMA) to maintain the
SNIR against interference signals due to cross-correlation from other users.

35 [0008] The channel estimation of data symbols obtains its channel estimates by averaging (coherently adding) pilot
symbols (estimated complex fading envelope) in a section (slot, in this case) to which the data symbols belong. The
channel estimation with high SNIR is carried out in this manner. The estimates are employed to detect with the pilot
symbols in the data symbol sections the received signal of a path of each user, to measure the amplitude and phase of
the signal of each path, and to estimate and compensate for the channel fluctuations in the data symbol sections.

40 [0009] However, it is difficult for the foregoing method disclosed in the paper to achieve highly accurate channel esti-
mation. This is because the method obtains the channel estimates by only averaging the pilot symbols in the slot includ-
ing the data symbols to be subjected to the channel estimation.

[0010] Furthermore, in an actual mobile transmission environment, thermal noise (reducing the transmission power
as low as possible creates a noise-limited environment, particularly at cell borders) and interference signals from other
45 users due to cross-correlation are added to a desired signal of the channel to be received, and the phase and amplitude
of the received signal vary every moment because of fading, which degrades the channel estimation accuracy In sum-
mary, it is difficult for the method disclosed in the foregoing paper, which carries out the channel estimation of the data
symbols using only the pilot symbols in the slot containing the data symbols, to achieve highly accurate channel esti-
mation.

50

DISCLOSURE OF THE INVENTION

[001 1] The present invention is implemented to solve the foregoing problems. It is therefore an object of the present
invention to achieve highly accurate channel estimation by obtaining highly accurate channel estimates by calculating
55 a sum of appropriately weighted pilot symbols when carrying out the channel estimation of the data symbols.

[001 2] Furthermore, the present invention can achieve higher accuracy channel estimation by carrying out the chan-
nel estimation of the data symbols using pilot symbols not only in the slot containing the data symbols, but also in other
slots.

2

EP 0 955 741 A1

[001 3] The highly accurate channel estimation and compensation for channel fluctuations in the data symbols based
on the channel estimation make it possible for the absolute coherent detection to decide the absolute phase of each
data symbol even in the Rayleigh fading environment, which can reduce the SNIR for achieving desired receiving qual-
ity (receiving error rate). This can reduce the transmission power, and increase the capacity of a system in terms of the
5 number of simultaneous subscribers.

[0014] In order to accomplish the object aforementioned, according to the invention as claimed in claim 1 , a channel
estimation unit for obtaining channel estimates of data symbols from a pilot symbol sequence which is parallel to a data
symbol sequence comprises:

10 means for generating a plurality of pilot blocks from the pilot symbol sequence; and

means for obtaining the channel estimates of the data symbols by calculating a weighted sum of averages of the
pilot symbols in the individual pilot blocks.

[0015] According to the invention as claimed in claim 2, a CDMA receiver which receives a data symbol sequence
15 that is spread, and a pilot symbol sequence that is spread and parallel to the data symbol sequence, and which gener-
ates a data sequence by demodulating the spread data symbol sequence by using the spread pilot symbol sequence
comprises:

means for receiving the spread data symbol sequence and the spread pilot symbol sequence;
20 means for generating a data symbol sequence by despreading the spread data symbol sequence;
means for generating a pilot symbol sequence by despreading the spread pilot symbol sequence;
means for generating from the pilot symbol sequence a plurality of pilot blocks;

means for obtaining channel estimates of the data symbols by calculating a weighted sum of averages of the pilot
symbols in the individual pilot blocks;
25 means for compensating for channel fluctuations in the data symbol sequence by using the channel estimates of
the data symbols; and

means for generating the data sequence by demodulating the data symbol sequence compensated for.

[0016] According to the invention as claimed in claim 3, in the CDMA receiver as claimed in claim 2, the spread data
30 symbol sequence has been spread using a first spreading code, the spread pilot symbol sequence has been spread
using a second spreading code, the means for generating the data symbol sequence despreads the spread data sym-
bol sequence which has been spread using the first spreading code, and the means for generating the pilot symbol
sequence despreads the spread pilot symbol sequence which has been spread using the second spreading code, and
wherein the first spreading code and the second spreading code are orthogonal to each other.
35 [0017] According to the invention as claimed in claim 4, a CDMA transceiver have a transmitting processor and a
receiving processor, the transmitting processor generate a spread data symbol sequence by modulating a data
sequence, and transmits the spread data symbol sequence with a spread pilot symbol sequence which is spread in par-
allel with the data symbol sequence, and the receiving processor receives the spread data symbol sequence and the
spread pilot symbol sequence, and generate the data sequence by demodulating the spread data symbol sequence by
40 using the spread pilot symbol sequence, wherein
the transmitting processor comprises:

means for generating the data symbol sequence by modulating the data sequence;
means for generating the spread data symbol sequence by spreading the data symbol sequence;
45 means for generating the spread pilot symbol sequence by spreading the pilot symbol sequence; and

means for transmitting the spread data symbol sequence and the spread pilot symbol sequence, and wherein
the receiving processor comprises:

means for receiving the spread data symbol sequence and the spread pilot symbol sequence;
means for generating the data symbol sequence by despreading the spread data symbol sequence;
50 means for generating the pilot symbol sequence by despreading the spread pilot symbol sequence;
means for generating from the pilot symbol sequence a plurality of pilot blocks;

means for obtaining channel estimates of the data symbols by calculating a weighted sum of averages of the pilot
symbols in the individual pilot blocks;

means for compensating for channel fluctuations in the data symbol sequence by using the channel estimates of
55 the data symbols; and

means for generating the data sequence by demodulating the data symbol sequence compensated for.

[001 8] According to the invention as claimed in claim 5, in the CDMA transceiver as claimed in claim 4, the means for

3

EP 0 955 741 A1

generating the spread data symbol sequence spreads the data symbol sequence using a first spreading code, the
means for generating the spread pilot symbol sequence spreads the pilot symbol sequence using a second spreading
code, the means for generating the data symbol sequence despreads the spread data symbol sequence which has
been spread using the first spreading code, and the means for generating the pilot symbol sequence despreads the
5 spread pilot symbol sequence which has been spread using the second spreading code, and wherein the first spread-
ing code and the second spreading code are orthogonal to each other.

[001 9] According to the invention as claimed in claim 6, in the CDMA transceiver as claimed in claim 4 or 5, the means
for transmitting the spread data symbol sequence and the spread pilot symbol sequence also transmits a spread power
control symbol sequence for controlling power of the data symbol sequence and that of the pilot symbol sequence.
10 [0020] According to the invention as claimed in claim 7, in the CDMA transceiver as claimed in claim 6, the transmit-
ting processor further comprises means for inserting into the data symbol sequence the power control symbol
sequence.

[0021] According to the invention as claimed in claim 8, in the CDMA transceiver as claimed in claim 6, the transmit-
ting processor further comprises means for inserting into the pilot symbol sequence the power control symbol
15 sequence.

[0022] According to the invention as claimed in claim 9, in the CDMA transceiver as claimed in claim 6, the transmit-
ting processor further comprises means for generating the spread power control symbol sequence by spreading the
power control symbol sequence, and the means for transmitting the spread data symbol sequence and the spread pilot
symbol sequence also transmits the power control symbol sequence.

20 [0023] According to the invention as claimed in claim 10, in the CDMA transceiver as claimed in claim 9, the means
for generating a spread data symbol sequence spreads the data symbol sequence by using a first spreading code, the
means for generating a spread pilot symbol sequence spreads the pilot symbol sequence by using a second spreading
code, and the means for generating a spread power control symbol sequence spreads the power control symbol
sequence by using a third spreading code, wherein the means for generating a data symbol sequence despreads the

25 spread data symbol sequence by using the first spreading code, the means for generating a pilot symbol sequence
despreads the spread pilot symbol sequence by using the second spreading code, and the means for generating a
power control symbol sequence despreads the spread power control symbol sequence by using the third spreading
code, and wherein the first spreading code, the second spreading code and the third spreading code are orthogonal to
each other.

30 [0024] According to the invention as claimed in claim 11 , in the CDMA transceiver as claimed in any one of claims 6-
10, the receiving processor further comprises means for measuring from the pilot symbol sequence a signal-to-noise
and interference power ratio, and for generating the power control symbol sequence from the signal-to-noise and inter-
ference power ratio.

[0025] According to the invention as claimed in claim 1 2, in the CDMA transceiver as claimed in any one of claims 4-
35 11, the receiving processor further comprises means for generating the power control symbol sequence by despread-
ing the spread power control symbol sequence for controlling the power of the data symbol sequence and that of the
pilot symbol sequence; and means for extracting the power control symbol sequence, and wherein the means for
receiving the spread data symbol sequence and the spread pilot symbol sequence receives the spread power control
symbol sequence, and the means for transmitting the spread data symbol sequence and the spread pilot symbol
40 sequence transmits the spread data symbol sequence and the spread pilot symbol sequence in accordance with the
power control symbol sequence.

[0026] According to the invention as claimed in claim 13, in the equipment as claimed in any one of claims 1 -12, the
power of the data symbol sequence and that of the pilot symbol sequence are controlled on a slot by slot basis, and
wherein the plurality of pilot blocks each consist of pilot symbols belonging to at least two different slots.
45 [0027] According to the invention as claimed in claim 1 4, in the equipment as claimed in any one of claims 1 -1 3, when
obtaining the channel estimate of an nth data symbol in the data symbol sequence, where n is an integer, the plurality
of the pilot blocks each consist of pilot symbols from (n-K+l) th pilot symbol to (n+K)th pilot symbol in the pilot symbol
sequence, where K is a natural number.

[0028] According to the invention as claimed in claim 15, in the equipment as claimed in any one of claims 1 -14, the
50 plurality of pilot blocks have a same length, each.

[0029] According to the invention as claimed in claim 1 6, in the equipment as claimed in any one of claims 1 -1 5, when
obtaining the channel estimate of an nth data symbol in the data symbol sequence, where n is an integer, the pilot
blocks consisting of pilot symbols closer to the nth pilot symbol have a greater weight.

[0030] According to the invention as claimed in claim 1 7, a channel estimation method for obtaining channel estimates
55 of data symbols from a pilot symbol sequence which is parallel with a data symbol sequence, comprises the steps of:

generating a plurality of pilot blocks from the pilot symbol sequence; and

obtaining the channel estimates of the data symbols by calculating a weighted sum of averages of the pilot symbols

4

EP 0 955 741 A1

in the individual pilot blocks.

[0031] According to the invention as claimed in claim 18, a CDMA receiving method which receives a data s/mbol
sequence that is spread, and a pilot s/mbol sequence that is spread and parallel to the data symbol sequence, and
5 which generates a data sequence by demodulating the spread data symbol sequence by using the spread pilot symbol
sequence comprises the steps of:

receiving the spread data symbol sequence and the spread pilot symbol sequence;
generating a data symbol sequence by despreading the spread data symbol sequence;
10 generating a pilot symbol sequence by despreading the spread pilot symbol sequence;
generating from the pilot symbol sequence a plurality of pilot blocks;

obtaining channel estimates of the data symbols by calculating a weighted sum of averages of the pilot symbols in
the individual pilot blocks;

compensating for channel fluctuations in the data symbol sequence by using the channel estimates of the data
15 symbols; and

generating the data sequence by demodulating the data symbol sequence compensated for.

[0032] According to the invention as claimed in claim 1 9, a CDMA transmitting and receiving method which generates
a spread data symbol sequence by modulating a data sequence, transmits the spread data symbol sequence with a
20 pilot symbol sequence which is spread in parallel with the data symbol sequence, receives the spread data symbol
sequence and the spread pilot symbol sequence, and generates the data sequence by demodulating the spread data
symbol sequence by using the spread pilot symbol sequence, wherein
a transmitting side comprises the steps of:

25 generating the data symbol sequence by modulating the data sequence;

generating the spread data symbol sequence by spreading the data symbol sequence;

generating the spread pilot symbol sequence by spreading the pilot symbol sequence; and

transmitting the spread data symbol sequence and the spread pilot symbol sequence, and wherein

a receiving side comprises the steps of:
30 receiving the spread data symbol sequence and the spread pilot symbol sequence;

generating the data symbol sequence by despreading the spread data symbol sequence;

generating the pilot symbol sequence by despreading the spread pilot symbol sequence;

generating from the pilot symbol sequence a plurality of pilot blocks;

obtaining channel estimates of the data symbols by calculating a weighted sum of averages of the pilot symbols
35 contained in the pilot blocks;

compensating for channel fluctuations in the data symbol sequence by using the channel estimates of the data
symbols; and

generating the data sequence by demodulating the data symbol sequence compensated for.
40 BRIEF DESCRIPTION OF THE DRAWINGS
[0033]

Fig. 1 is a block diagram showing a configuration of a channel estimation unit as a first embodiment in accordance
45 with the present invention;

Fig. 2 is a flowchart illustrating a channel estimation processing by the channel estimation unit of the first embodi-
ment in accordance with the present invention;

Fig. 3 is a diagram illustrating, taking an example of the channel estimation, the principle of operation of the channel
estimation by the channel estimation unit of the first embodiment in accordance with the present invention;
50 Fig. 4 is a block diagram showing a configuration of a CDMA receiver as a second embodiment in accordance with
the present invention;

Fig. 5 is a flowchart illustrating a receiving processing by the CDMA receiver of the second embodiment in accord-
ance with the present invention;

Fig. 6 is a block diagram showing a configuration of a CDMA transceiver as a third embodiment in accordance with
55 the present invention;

Fig. 7 is a block diagram showing a configuration of a transmitting processor of the CDMA transceiver of the third
embodiment in accordance with the present invention;

Fig. 8 is a block diagram showing a configuration of a receiving processor of the CDMA transceiver of the third

5

EP 0 955 741 A1

embodiment in accordance with the present invention;

Fig. 9 is a flowchart illustrating a transmitting processing by the transmitting processor of the CDMA transceiver of
the third embodiment in accordance with the present invention;

Fig. 10 is a diagram illustrating a transmission example which inserts power control symbols into a data symbol
5 sequence;

Fig. 1 1 is a diagram illustrating a transmission example which inserts power control symbols into a pilot symbol
sequence;

Fig. 12 is a diagram illustrating a transmission example which transmits power control symbols in a sequence apart
from the data symbol sequence and pilot symbol sequence; and
10 Fig. 13 is a diagram illustrating the principle of the channel estimation operation by a related art.

BEST MODE FOR CARRYING OUT THE INVENTION

[0034] Best modes for implementing the present invention will now be described in detail with reference to the accom-
15 panying drawings.

[FIRST EMBODIMENT]

[0035] Fig. 1 is a block diagram showing a configuration of a channel estimation unit as a first embodiment in accord-
20 ance with the present invention. A channel estimation unit 100 of the present embodiment obtains channel estimates
of data symbols from a pilot symbol sequence parallel with a data symbol sequence.

[0036] The channel estimation unit 100 comprises a pilot block generating section 1 1 0 and a channel estimate acqui-
sition section 120. Although the channel estimation unit 100 is implemented in the present embodiment in the form of
software using a DSP (Digital Signal Processor) (together with a memory that stores programs), it can be implemented
25 in the form of hardware, in which case, components such as delay circuits are used as needed.

[0037] Fig. 2 is a flowchart illustrating a channel estimation processing by the channel estimation unit of the present
embodiment, and Fig. 3 is a diagram illustrating, taking an example that obtains the channel estimates of an nth data
symbol (n is a natural number), the operation principle of the channel estimation unit of the present embodiment. In the
example of Fig. 3, both the data symbol sequence and the pilot symbol sequence undergo the transmission power con-
so trol on a slot by slot basis.

[0038] First, at step S201 , the pilot block generating section 110 generates from the pilot symbol sequence a plurality
of pilot blocks. To generate L (three, in this example) pilot blocks each with a length of X bits before and after the nth
pilot symbol, the example as shown in Fig. 3 uses pilot symbols from (n-K+1)th to (n+K)th pilot symbols, where
K=LxX is a natural number.

35 [0039] It is preferable to generate the pilot blocks from pilot symbols belonging to different multiple slots to use these
plot symbols for the channel estimation. Using pilot symbols of different slots has an advantage of reducing the effect
of the thermal noise and interference signals, which is greater than channel estimation error due to differences in power
between the pilot symbols of different slots, making it possible to achieve the channel estimation at higher accuracy In
the example as shown in Fig. 3, six pilot blocks are generated from pilot symbols belonging to seven slots.

40 [0040] To obtain the channel estimate of the nth data symbol, it is not necessary to generate the same number of pilot
blocks before and after the nth pilot symbol as in the example of Fig. 3. Thus, considering the delay of the channel esti-
mation, the pilot blocks can be generated only from the pilot symbols with the number smaller than (previous to) the nth
pilot symbol.

[0041] The length of a pilot block can be determined independently of the length of a slot. For example, the length of
45 a pilot block can be equal to that of a pilot symbol, that is, a pilot block can consist of a single pilot symbol. Besides, the
length of a pilot block can be varied from block to block.

[0042] At steps S202-S204, the channel estimate acquisition section 120 obtains the channel estimates of the data
symbols. First, at step S202, the channel estimate acquisition section 120 calculates an average of the pilot symbols %
(estimated complex fading envelope) in each pilot block to obtain the pilot block average |, which is carried out for all
50 the pilot blocks (step S203). When each pilot block consists of only one pilot symbol, the pilot symbol I itself becomes
the pilot symbol average |. In the example of Fig. 3, the pilot block averages | (nj) are each obtained for ith pilot blocks
(i = -L toL,i^).

[0043]^ At step S204, the channel estimate acquisition section 1 20 calculates the weighted sum of the pilot block aver-
ages I to obtain the channel estimates | of the data symbol. In the example of Fig. 3, the channel estimate I (n) of the
55 nth data symbol is obtained by placing the weights of the ith blocks at a(nj). The channel estimate I (n) is given by the
following equation (1).

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EP 0 955 741 A1

|(n)= i a(n.)i(n,) (1)

5

[0044] It is preferable to increase the weights a{n) of the pilot blocks that include pilot symbols closer (closer in time)
to the nth pilot symbol. This is because such pilot blocks can be considered to represent the state of the propagation
10 path during the transmission of the nth data symbol more correctly because the propagation path fluctuates at every
moment.

[0045] The channel estimate acquisition section 120 iterates the foregoing steps S201 - S204 for all the data symbols
with which the channel estimates must be obtained (step S205).
[0046] Thus, highly accurate channel estimates can be obtained.

15

[SECOND EMBODIMENTI

[0047] Fig. 4 is a block diagram showing a configuration of a CDMA receiver as a second embodiment in accordance
with the present invention. A CDMA receiver 400 of the present embodiment receives a data symbol sequence which

20 is spread, and a pilot symbol sequence which is spread and parallel to the data symbol sequence, and restores the data
sequence by demodulating the spread data symbol sequence using the spread pilot symbol sequence.
[0048] The CDMA receiver 400 comprises a receiving section 41 0, a data symbol sequence matched filter 424, a pilot
symbol sequence matched filter 426, a channel estimation processor 428, a data symbol sequence compensator 430,
a RAKE combiner 432, a deinterleaver 434 and a Viterbi decoder 436. Although these components such as the data

25 symbol sequence matched filter 424, pilot symbol sequence matched filter 426 and so forth are implemented in the
form of software using a DSP (and a memory that stores programs) 420 as shown in Fig. 4 in the present embodiment,
they can be implemented with hardware. The structure and functions of the channel estimation processor 428 are the
same as those of the channel estimation unit 100 of the first embodiment in accordance with the present invention.
[0049] Fig. 5 is a flowchart illustrating a receiving processing by the CDMA receiver of the second embodiment in

30 accordance with the present invention. First, at step S501 , the receiving section 410 receives the received signal, that
is, the spread data symbol sequence and the spread pilot symbol sequence.

[0050] In the present embodiment, it is assumed that the received data symbol sequence and pilot symbol sequence
have been spread using a first spreading code and a second spreading code, respectively, which are orthogonal to
each other. At step S502, the data symbol sequence matched filter 424 despreads the received signal using the first

35 spreading code, thereby generating the data symbol sequence. At step S503, the pilot symbol sequence matched filter
426 despreads the received signal using the second spreading code, thereby generating the pilot symbol sequence.
[0051] At step S504, the channel estimation processor 428 carries out a channel estimation processing to obtain the
channel estimates of the data symbols. The channel estimation processing is the same as that of the channel estima-
tion unit 100 (Fig. 2) of the first embodiment in accordance with the present invention.

40 [0052] At step S505, the data symbol sequence compensator 430 compensates for the channel fluctuations in the
data symbol sequence using the channel estimates f . More specifically, it compensates for the channel fluctuations in
the data symbols by multiplying the data symbol sequence by the complex conjugates of the channel estimates ^
[0053] At step S506, the RAKE combiner 432, deinterleaver 434 and Viterbi decoder 436 generates the data
sequence by demodulating the compensated data symbol sequence. The RAKE combiner 432 carries out the in-phase

45 combining of the compensated data symbol sequence fed from individual RAKE fingers.

[0054] Thus, the receiving processing can achieve highly accurate channel estimation, and the compensation for the
channel fluctuations in the data symbol sequence.

[THIRD EMBODIMENT!

50

[0055] Fig. 6 is a block diagram showing a configuration of a CDMA transceiver as a third embodiment in accordance
with the present invention. A CDMA transceiver 600 of the present embodiment comprises a transmitting processor 610
and a receiving processor 620. The transmitting processor 610 generates a spread data symbol sequence by modulat-
ing a data sequence, and transmits the spread data symbol sequence along with a pilot symbol sequence which is par-
55 allel with the data symbol sequence and undergoes spreading. The receiving processor 620 receives the spread data
symbol sequence and the spread pilot symbol sequence, and demodulates the spread data symbol sequence using the
spread pilot symbol sequence to generate the data sequence. In the present embodiment, this station (the present
CDMA transceiver) exchanges power control symbols with a party station. The power control symbols are symbols

7

EP 0 955 741 A1

(command) for controlling power of the data symbol sequence and the pilot symbol sequence.
[0056] Fig. 7 shows a configuration of the transmitting processor 610, and Fig. 8 shows a configuration of the receiv-
ing processor.

[0057] As shown in Fig. 7, the transmitting processor 610 comprises a transmitting section 710, a channel encoder
5 722, an inserting section 724, a data symbol sequence spreader 726, a pilot symbol sequence spreader 728 and a
combiner 730. Although these components such as the channel encoder 722, inserting section 724 and so forth are
implemented in the form of software using a DSP (and a memory that stores programs) 720 in the present embodiment,
they can be implemented with hardware.

[0058] Fig. 9 is a flowchart illustrating a transmitting processing by the transmitting processor of the CDMA transceiver
10 of the present embodiment. First, at step S901 , the channel encoder 722 generates the data symbol sequence by mod-
ulating (encoding) the data sequence.

[0059] At step S902, the inserting section 724 inserts into the data symbol sequence the power control symbol
sequence the party station uses to determine the power of a data symbol sequence and a pilot symbol sequence to be
transmitted from the party station to the present station.
15 [0060] Fig. 10 is a diagram illustrating an example that inserts the power control symbols into the data symbol
sequence to be transmitted, in which case, the power control symbols are inserted into the data symbol sequence at
every one-slot interval.

[0061] Although the power control symbols are inserted into the data symbol sequence to be transmitted in the
present embodiment, they can be inserted into the pilot symbol sequence to be transmitted, or they can be transmitted

20 as another sequence in addition to the data symbol sequence and pilot symbol sequence, as will be described later.
[0062] Returning to Fig. 9, at step S903, the data symbol sequence spreader 726 spreads the data symbol sequence
using the first spreading code to generate the spread data symbol sequence. At step S904, the pilot symbol sequence
spreader 728 spreads the pilot symbol sequence using the second spreading code to generate the spread pilot symbol
sequence. The first spreading code and the second spreading code are orthogonal to each other.

25 [0063] At step S905, the combiner 730 combines the spread data symbol sequence and the spread pilot symbol
sequence to generate a transmitted signal.

[0064] At step S906, the transmitting section 710 transmits the transmitted signal in accordance with a power control
symbol sequence which is sent from the party station to the present station.

[0065] Next, as shown in Fig. 8, the receiving processor 620 comprises a receiving section 810, a data symbol

30 sequence matched filter 824, a pilot symbol sequence matched filter 826, a channel estimation processor 828, a data
symbol sequence compensator 830, a RAKE combiner 832, a deinterleaver 834, a Viterbi decoder 836, a power control
symbol generator 838 and a power control symbol sequence extracting section 840. Although these components such
as the data symbol sequence matched filter 824, pilot symbol sequence matched filter 826 and so forth are imple-
mented in the form of software using a DSP (and a memory that stores programs) 820 in the present embodiment, they

35 can be implemented with hardware. The structure and functions of the channel estimation processor 828 are the same
as those of the channel estimation unit 100 of the first embodiment in accordance with the present invention, and the
structure and functions of the receiving section 810, data symbol sequence matched filter 824 and so forth are the
same as those of their counterparts of the CDMA receiver of the second embodiment. Accordingly, the receiving proc-
essor 620 carries out the same processings as those (Fig. 5) of the CDMA receiver of the second embodiment in

40 accordance with the present invention.

[0066] The power control symbol generator 838 measures the SNIR from the pilot symbol sequence supplied from
the pilot symbol sequence matched filter 826, and generates the power control symbols in response to the measured
values. As a measuring method of the SNIR, there is a method of measuring it by obtaining the average and variance
of the received signal. The SNIR measurement can also use feedback data symbol sequence after decision. The power

45 control symbols generated here are supplied to the inserting section 724 of the transmitting processor 610, which
inserts them into the data symbol sequence when transmitting the next signal to the party station to be transmitted.
Receiving the symbols, the party station uses them when transmitting a signal to the present station.
[0067] The power control symbol sequence extracting section 840 extracts from the data symbol sequence the power
control symbol sequence, and supplies it to the transmitting section 710 of the transmitting processor 610 to be used

50 when transmitting the next signal to the party station.

[0068] The power control symbols can also be inserted into the pilot symbol sequence. Fig. 11 is a diagram illustrating
a transmission example in which power control symbols are inserted into a pilot symbol sequence to be transmitted. To
insert the power control symbols into the pilot symbol sequence, a component corresponding to the inserting section
724 is installed in the transmitting processor 610 so that it inserts into the pilot symbol sequence the power control sym-

55 bol sequence, and a component corresponding to the power control symbol sequence extracting section 840 is installed
in the receiving processor 620 so that it extracts from the pilot symbol sequence the power control symbol sequence.
[0069] The power control symbols can be transmitted as another sequence in addition to the data symbol sequence
and the pilot symbol sequence. Fig. 12 is a diagram illustrating a transmission example in which the power control sym-

8

EP 0 955 741 A1

bols are transmitted in a sequence apart from the data symbol sequence and pilot symbol sequence. To transmit the
power control symbols in a sequence besides the data symbol sequence and pilot symbol sequence, a means for
spreading the power control symbols is provided in the transmitting processor 610. The spread power control symbol
sequence is combined with the spread data symbol sequence and the spread pilot symbol sequence to be transmitted.
5 To spread the power control symbol sequence, a third spreading code is used which is orthogonal to the first spreading
code used for spreading the data symbol sequence and to the second spreading code used for spreading the pilot sym-
bol sequence. The receiving processor 620 is provided with a means for despreading the power control symbol
sequence, and receives the spread power control symbol sequence and despreads it.

[0070] The transmission of the power control symbol sequence can be unidirectional rather than bidirectional. For
10 example, the power control symbol sequence can be transmitted only from a base station to a mobile station to control
the (transmission) power of only a reverse channel (from the mobile station to the base station) in communications
between the two stations.

[0071] Thus, the transceiver can achieve in its processing highly accurate channel estimation and compensation for
the channel fluctuations in the data symbol sequence.
15 [0072] As described above, the present invention can achieve, when performing the channel estimation of the data
symbols, the highly accurate channel estimation by obtaining highly accurate channel estimates by calculating the sum
of the pilot symbols which are appropriately weighted.

[0073] In addition, using the pilot symbols in the slots other than the slot including the data symbols to be estimated,
the channel estimation of the data symbols can further improve its accuracy
20 [0074] The highly accurate channel estimation together with the compensation for the channel fluctuations in the data
symbols on the basis of the channel estimation makes it possible to decide the absolute phases of individual data sym-
bols by using the absolute coherent detection, and to reduce the SNIR needed for achieving the desired receiving qual-
ity (receiving error rate). As a result, the transmission power can be reduced, and the capacity of the system in terms
of the number of subscribers can be increased.

25

Claims

1. A channel estimation unit for obtaining channel estimates of data symbols from a pilot symbol sequence which is
parallel to a data symbol sequence, said channel estimation unit characterized by comprising:

30

means for generating a plurality of pilot blocks from the pilot symbol sequence; and

means for obtaining the channel estimates of the data symbols by calculating a weighted sum of averages of
the pilot symbols in the individual pilot blocks.

35 2. A CDMA receiver which receives a data symbol sequence that is spread, and a pilot symbol sequence that is
spread and parallel to the data symbol sequence, and which generates a data sequence by demodulating the
spread data symbol sequence by using the spread pilot symbol sequence, said CDMA receiver characterized by
comprising:

40 means for receiving the spread data symbol sequence and the spread pilot symbol sequence;

means for generating a data symbol sequence by despreading the spread data symbol sequence;
means for generating a pilot symbol sequence by despreading the spread pilot symbol sequence;
means for generating from the pilot symbol sequence a plurality of pilot blocks;

means for obtaining channel estimates of the data symbols by calculating a weighted sum of averages of the
45 pilot symbols in the individual pilot blocks;

means for compensating for channel fluctuations in the data symbol sequence by using the channel estimates
of the data symbols; and

means for generating the data sequence by demodulating the data symbol sequence compensated for.

50 3. The CDMA receiver as claimed in claim 2, characterized in that the spread data symbol sequence has been spread
using a first spreading code, the spread pilot symbol sequence has been spread using a second spreading code,
said means for generating the data symbol sequence despreads the spread data symbol sequence which has been
spread using the first spreading code, and said means for generating the pilot symbol sequence despreads the
spread pilot symbol sequence which has been spread using the second spreading code, and characterized in that

55 the first spreading code and the second spreading code are orthogonal to each other.

4. A CDMA transceiver having a transmitting processor and a receiving processor, said transmitting processor gener-
ating a spread data symbol sequence by modulating a data sequence, and transmitting the spread data symbol

9

EP 0 955 741 A1

sequence with a spread pilot symbol sequence which is spread in parallel with the data symbol sequence, and said
receiving processor receiving the spread data symbol sequence and the spread pilot symbol sequence, and gen-
erating the data sequence by demodulating the spread data symbol sequence by using the spread pilot symbol
sequence, wherein
5 said transmitting processor comprises:

means for generating the data symbol sequence by modulating the data sequence;
means for generating the spread data symbol sequence by spreading the data symbol sequence;
means for generating the spread pilot symbol sequence by spreading the pilot symbol sequence; and
10 means for transmitting the spread data symbol sequence and the spread pilot symbol sequence, and wherein

said receiving processor comprises:

means for receiving the spread data symbol sequence and the spread pilot symbol sequence;
means for generating the data symbol sequence by despreading the spread data symbol sequence;
means for generating the pilot symbol sequence by despreading the spread pilot symbol sequence;
15 means for generating from the pilot symbol sequence a plurality of pilot blocks;

means for obtaining channel estimates of the data symbols by calculating a weighted sum of averages of the
pilot symbols in the individual pilot blocks;

means for compensating for channel fluctuations in the data symbol sequence by using the channel estimates
of the data symbols; and

20 means for generating the data sequence by demodulating the data symbol sequence compensated for.

5. The CDMA transceiver as claimed in claim 4, characterized in that said means for generating the spread data sym-
bol sequence spreads the data symbol sequence using a first spreading code, said means for generating the
spread pilot symbol sequence spreads the pilot symbol sequence using a second spreading code, said means for
25 generating the data symbol sequence despreads the spread data symbol sequence which has been spread using
the first spreading code, and said means for generating the pilot symbol sequence despreads the spread pilot sym-
bol sequence which has been spread using the second spreading code, and characterized in that the first spread-
ing code and the second spreading code are orthogonal to each other.

30 6. The CDMA transceiver as claimed in claim 4 or 5, characterized in that said means for transmitting the spread data
symbol sequence and the spread pilot symbol sequence also transmits a spread power control symbol sequence
for controlling power of the data symbol sequence and that of the pilot symbol sequence.

7. The CDMA transceiver as claimed in claim 6, characterized in that said transmitting processor further comprises
35 means for inserting into the data symbol sequence the power control symbol sequence.

8. The CDMA transceiver as claimed in claim 6, characterized in that said transmitting processor further comprises
means for inserting into the pilot symbol sequence the power control symbol sequence.

40 9. The CDMA transceiver as claimed in claim 6, characterized in that said transmitting processor further comprises
means for generating the spread power control symbol sequence by spreading the power control symbol
sequence, and said means for transmitting the spread data symbol sequence and the spread pilot symbol
sequence also transmits the power control symbol sequence.

45 10. The CDMA transceiver as claimed in claim 9, characterized in that said means for generating a spread data symbol
sequence spreads the data symbol sequence by using a first spreading code, said means for generating a spread
pilot symbol sequence spreads the pilot symbol sequence by using a second spreading code, and said means for
generating a spread power control symbol sequence spreads the power control symbol sequence by using a third
spreading code, characterized in that said means for generating a data symbol sequence despreads the spread

50 data symbol sequence by using the first spreading code, said means for generating a pilot symbol sequence
despreads the spread pilot symbol sequence by using the second spreading code, and said means for generating
a power control symbol sequence despreads the spread power control symbol sequence by using the third spread-
ing code, and characterized in that the first spreading code, the second spreading code and the third spreading
code are orthogonal to each other.

55

1 1 . The CDMA transceiver as claimed in any one of claims 6-10, characterized in that said receiving processor further
comprises means for measuring from the pilot symbol sequence a signal-to-noise and interference power ratio, and
for generating the power control symbol sequence from the signal-to-noise and interference power ratio.

10

EP 0 955 741 A1

12. The CDMA transceiver as claimed in any one of claims 4-1 1 , characterized in that said receiving processor further
comprises means for generating the power control symbol sequence by despreading the spread power control
symbol sequence for controlling the power of the data symbol sequence and that of the pilot symbol sequence; and
means for extracting the power control symbol sequence, and characterized in that said means for receiving the
5 spread data symbol sequence and the spread pilot symbol sequence receives the spread power control symbol

sequence, and said means for transmitting the spread data symbol sequence and the spread pilot symbol
sequence transmits the spread data symbol sequence and the spread pilot symbol sequence in accordance with
the power control symbol sequence.

10 13. The equipment as claimed in any one of claims 1 -12, characterized in that the power of the data symbol sequence
and that of the pilot symbol sequence are controlled on a slot by slot basis, and characterized in that the plurality
of pilot blocks each consist of pilot symbols belonging to at least two different slots.

14. The equipment as claimed in any one of claims 1-13, characterized in that when obtaining the channel estimate of
15 an nth data symbol in the data symbol sequence, where n is an integer, the plurality of the pilot blocks each consist

of pilot symbols from (n-K-i-l)th pilot symbol to (n+K)th pilot symbol in the pilot symbol sequence, where K is a nat-
ural number.

15. The equipment as claimed in any one of claims 1 -14, characterized in that the plurality of pilot blocks have a same
20 length, each.

16. The equipment as claimed in any one of claims 1-15, characterized in that when obtaining the channel estimate of
an nth data symbol in the data symbol sequence, where n is an integer, the pilot blocks consisting of pilot symbols
closer to the nth pilot symbol have a greater weight.

25

M. IK channel estimation method for obtaining channel estimates of data symbols from a pilot symbol sequence which
is parallel with a data symbol sequence, said channel estimation method characterized by comprising the steps of:

generating a plurality of pilot blocks from the pilot symbol sequence; and
30 obtaining the channel estimates of the data symbols by calculating a weighted sum of averages of the pilot

symbols in the individual pilot blocks.

18. A CDMA receiving method which receives a data symbol sequence that is spread, and a pilot symbol sequence
that is spread and parallel to the data symbol sequence, and which generates a data sequence by demodulating

35 the spread data symbol sequence by using the spread pilot symbol sequence, said CDMA receiving method char-
acterized by comprising the steps of:

receiving the spread data symbol sequence and the spread pilot symbol sequence;
generating a data symbol sequence by despreading the spread data symbol sequence;
40 generating a pilot symbol sequence by despreading the spread pilot symbol sequence;

generating from the pilot symbol sequence a plurality of pilot blocks;

obtaining channel estimates of the data symbols by calculating a weighted sum of averages of the pilot sym-
bols in the individual pilot blocks;

compensating for channel fluctuations in the data symbol sequence by using the channel estimates of the data
45 symbols; and

generating the data sequence by demodulating the data symbol sequence compensated for.

19. A CDMA transmitting and receiving method which generates a spread data symbol sequence by modulating a data
sequence, transmits the spread data symbol sequence with a pilot symbol sequence which is spread in parallel

50 with the data symbol sequence, receives the spread data symbol sequence and the spread pilot symbol sequence,
and generates the data sequence by demodulating the spread data symbol sequence by using the spread pilot
symbol sequence, wherein
a transmitting side comprises the steps of:

55 generating the data symbol sequence by modulating the data sequence;

generating the spread data symbol sequence by spreading the data symbol sequence;
generating the spread pilot symbol sequence by spreading the pilot symbol sequence; and
transmitting the spread data symbol sequence and the spread pilot symbol sequence, and wherein

11

EP 0 955 741 A1

a receiving side comprises tine steps of:

receiving the spread data symbol sequence and tlie spread pilot symbol sequence;
generating the data symbol sequence by despreading the spread data symbol sequence;
generating the pilot symbol sequence by despreading the spread pilot symbol sequence;
generating from the pilot symbol sequence a plurality of pilot blocks;

obtaining channel estimates of the data symbols by calculating a weighted sum of averages of the pilot sym-
bols contained in the pilot blocks;

compensating for channel fluctuations in the data symbol sequence by using the channel estimates of the data
symbols; and

generating the data sequence by demodulating the data symbol sequence compensated for.

EP 0 955 741 A1

EP 0 955 741 A1

Q START ^

S201

GENERATE FROM PILOT SYMBOL
SEQUENCE A PLURALITY OF
PILOT BLOCKS

CALCULATE AN AVERAGE OF

PILOT SYMBOLS IN EACH
PILOT BLOCK TO OBTAIN A
PILOT BLOCK AVERAGE

S202

OBTAIN A CHANNEL ESTIMATE
OF EACH DATA SYMBOL

BY CALCULATING A
WEIGHTED SUM OF THE
PILOT BLOCK AVERAGES

S204

FIG.2

14

EP 0 955 741 A1

15

EP 0 955 741 A1

16

EP 0 955 741 A1

START ^

RECEIVE RECEIVED SIGNAL
(SPREAD DATA SYMBOL SEQUENCE

AND SPREAD PILOT SYMBOL
SEQUENCE)

GENERATE DATA SYMBOL
SEQUENCE BY DESPREADING
RECEIVED SIGNAL

GENERATE PILOT SYMBOL

SEQUENCE BY
DESPREADING RECEIVED
SI^IAL

CARRY OUT CHANNEL
ESTIMATION PROCESSING TO
OBTAIN CHANNEL ESTIMATES
OF DATA SYMBOLS

COMPENSATE FOR CHANNEL
FLUCTUATIONS IN DATA SYMBOL
SEQUENCE USING CHANNEL
ESTIMATES

GENERATE DATA SEQUENCE BY
DEMODULATING DATA SYMBOL
SEQUENCE COMPENSATED FOR

END ^

FIG. 5

EP 0 955 741 A1

600

CDMA TRANSCEIVER

610

TRANSMITTING
PROCESSOR

620

RECEIVING
PROCESSOR

FIG. 6

18

EP 0 955 741 A1

O

OHOi
l-l

CO

Pi

19

EP 0 955 741 A1

20

EP 0 955 741 A1

Q START ^

GENERATE DATA SYMBOL
SEQUENCE BY MODULATING DATA
SEQUENCE

S901

INSERT INTO DATA SYMBOL
SEQUENCE POWER CONTROL
SYMBOL SEQUENCE

S902

GENERATE SPREAD DATA

SYMBOL SEQUENCE BY
SPREADING DATA SYMBOL
SEQUENCE

S903

GENERATE SPREAD PILOT

SYMBOL SEQUENCE BY
SPREADING PILOT SYMBOL
SEQUENCE

I

S904

GENERATE TRANSMITTED
SIGNAL BY COMBINING SPREAD
DATA SYMBOL SEQUENCE AND
SPREAD PILOT SYMBOL SEQUENCE

S905

S906

TRANSMIT TRANSMITTED
SIGNAL

i

END ^

FIGS

21

EP 0 955 741 A1

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EP 0 955 741 A1

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EP 0 955 741 A1

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25

EP 0 955 741 A1

INTERNATIONAL SEARCH REPORT

bitemational application No,

PCT/JP98/05241

A OASSmCATION OF SUBJECT MATTER
int. CI* H04J13/00

Aocording to International Patent Claagificatioti (IPQ or to both national classificatioo and IPC
B, FIELDS SEARCHED

Minimum docuraentation searched (classification syitem followed by classification syaU>ol8)
Int. CI* H04J13/00

Documentation searcfaed other than minimum documentation to the extent that such documents are included in the fiekis searched

Jitsuyo Shinon Volx> CY1« Y2) 1926-1999 Tbroku Jitsuyo Shiiwn KoIk> <U) 1994-1999
Kokai JitBizyo Shinan Hoho (U) 1971-1999 Jitsuyo Shlnon Torc^ Koho (Y2) 1996-1999

Electronic data base consulted duriiiig the intematianAl search (name of dau base and, where praaicable^ search terms used)

C DOCUMEN-re CONSIDBRHD TO BE RELEVANT

Category*

Citation of dacument, with indication, where appropriate, of the relevant

Relevant to daim No.

PA

PA

JP, 10-51424, A (NTT Mobile Communications Network
inc . ) ,

20 February^ 1998 (20. 02. 98),

Par. Nos. [0012], [0018] to [0021] ? Figs. 1, 3
( Family : none )

JP, 10-190494, A (Fujitsu Ltd.)*

21 July, 1998 (21. 07. 98),

Par. Noa. [0031] to [0044] (Family; none)

JP, 9-8770, A (Matsushita Electric Industrial Co.,
Ltd. ) ,

10 January, 1997 (10. 01. 97),

Par. Nos. [0009], [0010] ; Fig. 1 (Family: none)

JP, 7-221700, A (Matsushita Electric Industrial
Co., Ltd.),

18 August, 1995 (18. 08. 95),
Par. Nos. [0010], [0011] ; Fig. 1
& EP, Al, 668654 & JP, A, 7226710
& CA, h, 2139919 & US, A, 5559789

1-19

1-19

1-19

11

Px] Further documents are listed in the oontinuation of Box C. See patent family annex.

•A'

Spedft] cat^orics of cii

docomcait defiainc the senetal ttatcof the anwhidi is not
cxMoMiered lo be of putkalu- relevsine
*£" eaitierdocaaieatbaipubliriMoaur after the iolentationalf^^
*L* docaneatwhictinay thfw doubts oapriohtydaMB) or whl
died Eo estabKsh Ihe pubUcatkm dale of another dtation or other
^MOB] leaaoa (as specified)
"O' doaaneni fcfennig to an ml diaclosan; awt, cxhiMtimi or otiicr

*P" dooaaiBtttpMbUdwd prior to the mlernatioaal filing date but later tim
the i»nonty datecteiaMd

"T UlerdcKraaMatpiibliihedallef tbatniemtkMntrdhigdatftdrp^^

date and Mt ift cooCUct wkh the sn^tiott but died to oadMilaad

lh« priodple or theory udcrlyiog the invenrioB
'X* docunitafparticatef rejevawx; theciaiittediflmtioacaaDOtbe

unaiklBicd novel or cmudI be ooiuid cf cd fa lOvoKe an tnvcnlhw stop

when the dociWKiat is taken aloae
"Y" dcKnmem of particular ftlmaoe; the ciairaediiivcattcwcatw^

ocMirideRd to iavoKe an hiveiiiive step when the docunieai b

a>«binedwift one or more odteisiHlidocmiMW such ownbiaatiw

bang efnrioiu to a peraoo skilled m the an
"A" document moaberirf the laaie patent £»mtly

Date of the actual completion of the international search
10 February, 1999 (10. 02. 99)

Date of mailing of the international search report

23 February, 1999 (23. 02. 99)

Name add mailing address of the ISA/

Japanese patent Office

Facsimile No.

Authorized officer

Teiepfione No.

Foim VCT/lSA/llQ (second sheet) (July 1992)

26

EP 0 955 741 A1

INTERNATIONAL SEARCH REPORT

IntenULticxLAl applicfttion No.

PCT/JP98/05241

C (Continuation). DOCUMENTS CONSIDERED TO BE REIPVANT

Category*

QtatKA of docmnent, with ifidkatjon, where a|»propriate, of the relevant passages

Relevant to daim No.

JP, 8-88589 r A (Hitachi Ltd. ) /
2 April, 1996 (02. 04. 96),
Par. No. [0036] } Pig. l

ZP, A2, 693830 & OA, A, 2153516
fc US, A, 5666352 & CN, A, 1118976

3, 5

Form P(7r/ISA/210 (cootiouatioD of second sheet) (July 1992)

27